As a steam power cycle system that cycles a working fluid, while heating and cooling it, and causes the working fluid repeating a phase change to work, thus obtaining a power, there is generally known a basic type of Rankine cycle that is provided with an evaporator, a turbine, a condenser and a pump, and utilizes water as the working fluid.
However, in order to make a proper phase change of the working fluid to convert effectively heat into power, in case where, in using the steam power cycle as a power generating equipment, etc., a temperature of both a high-temperature heat source and a low-temperature heat source in the steam power cycle is lower than a boiling point of water, in particular, in the application to a power generation apparatus by an ocean thermal energy conversion, and a difference in temperature between the heat sources is small, there has conventionally been proposed a steam power cycle such as Rankine cycle in which a common water is not used, but a fluid such as ammonia having a lower boiling point than water is used as the working fluid, or Kalina cycle in which, there is used, as the working fluid, a mixture medium that has been prepared by mixing water and kinds of fluids having different boiling points from each other so as to make the boiling point of it than water.
Concerning an example of the conventional Rankine cycle using the working fluid having a low boiling point, JP 52-156246 A discloses a power generation apparatus by an ocean thermal energy conversion, and JP 5-340342 A discloses a power generation apparatus by an ocean thermal energy conversion with three cycles. In addition, JP 57-200607 describes an example of a steam power cycle in which the conventional mixture medium is used as the working fluid.